Method and apparatus for forming, filling and sealing bags made from a continuous plastic sheet

ABSTRACT

A plastic bag is formed, filled, sealed and separated from a continuous web of longitudinally folded plastic material. The web passes downwardly between complementary L-shaped heat sealing jaws that reciprocate and cooperate to provide seams which form a pocket that is closed after it has been filled from above and indexed downwardly. The top seam of one pocket is formed simultaneously with the bottom seam of an adjacent pocket and a weakened line of juncture is provided therebetween. Grippers carried on the heat sealing jaws engage opposite sides of the plastic web above the location of the top seam of the filled pocket and cooperate with a separator that tensions the web along the weakened line to rupture the filled pocket from the web while the web is still in a thermally weakened condition.

FIELD OF THE INVENTION

The present invention relates to bag forming, filling and sealingmethods and machinery, and more particularly, the present inventionrelates to a method and apparatus for forming and filling bags from acontinuous sheet of plastic material.

BACKGROUND OF THE INVENTION

Methods and apparatus are known for forming, filling and sealing bagsformed from a continuous sheet of material. In conventional apparatus, afolded sheet of vertically disposed material is advanced longitudinallyand heat sealed to form a bag, or pouch, which is gravitationally loadedby means of a declining chute connected to an elevated hopper. After thebag has been formed and loaded, its upper end is seamed to completelyseal the bag. The thus filled bag is subsequently severed from the web.Machines of this general nature are disclosed in the following U.S. Pat.Nos.: 2,334,256; 2,385,229; 3,426,499; 3,731,451; 3,815,318; 4,144,693;4,235,064; 4,322,929; and 4,391,081. Other types of packaging machinesare disclosed in U.S. Pat. Nos. 3,319,538 and 3,397,505. Related typesof commercially available packaging machines are sold by Rennco, Inc. ofHomer, Mich.; Automated Packaging Systems, Inc. of Twinsburg, Ohio; andBodolay-Pratt of Lakeland, Fla.

A limiting factor in the reliability of a plastic bag forming a fillingmachine resides in the means utilized to separate the filled bag fromthe web from which it is formed. Known machines use knives, hot wires,and the like to effect separation. These separating mechanisms areundesirable, however, because the plastic accumulates thereon and causesthem to malfunction. As a result, the machinery must be stoppedperiodically and cleared.

Another acute problem is caused by the composition and quality of theplastic composing the web. For instance, when hot knives and wires areused as the bag separating means, their proper functioning is dependenton the composition and quality of the plastic, since different plasticmaterials, and variations in quality with a given roll of plastic,change the heat requirements needed to effect proper bag separation.This creastes further machine set-up and operating problems. Inaddition, the burning of the material by the hot wires causesundesirable fumes to be generated, and this is unsatisfactory.

While each of the aforedescribed patented and commercially availablemachines may function satisfactorily for its intended purpose, there isa need for machinery which can operate in a reliable method with minimalmaintenance to form, fill and seal bags made from a continuous web ofplastic at relatively high rates of production. Furthermore, there is aneed for a machine of the aforedescribed type which is tolerant ofvariations in plastic composition and quality and which can operate witha minimum of downtime and with a minimum of operator adjustments.Moreover, a commercially-desirable machine should also be capable ofbeing run by a relatively unskilled operator.

OBJECTS OF THE INVENTION

With the foregoing in mind, a primary object of the present invention isto provide a novel method and apparatus for forming, and filling andsealing bags made from a continuous sheet of plastic, and of doing so atrelatively high production rates.

Another object of the present invention is to provide an improved methodand apparatus for reliably producing filled plastic bags in atrouble-free manner at relatively high production rates.

A further object of the present invention is to provide a unique bagforming, filling and sealing machine which operates smoothly andreliably for prolonged periods of time with minimal operatorintervention.

As a still further object, the present invention provides an efficientmachine which operates in a novel manner to form, fill, seal, and severbags from a continuous web of plastic.

SUMMARY OF THE INVENTION

More specifically, in the present invention, bags are formed, filled,sealed and severed in a high speed trouble-free manner from a continuousweb of folded plastic material as it advances downwardly through themachine frame. Complementary L-shaped heat sealing jaws are mounted inthe frame for lateral reciprocation with respect to opposite sides ofthe web for providing a bottom seam, a side seam, and a top seam afterthe bag has been filled. The top and bottom seams are provided by aspecially-shaped heater bar and anvil which cooperate simultaneously toprovide the bottom seam of one pocket and the top seam of a downstreampocket while forming a weakened line of juncture therebetween. Thefilled bag is then separated from the web by downward tension whichruptures the web along the weakened line of juncture. Downward tensionis applied by a roller which is biased into engagement with the web androtated about is axis when a counterbiased nip platen is pivotedrelative to the roller axis. In the illustrated embodiment, thelongitudinal side seam extends inwardly of the folded edges of theplastic web and the edge margin is continuously separated from theplastic web by a constant tensioning device which pulls downwardly andlaterally on the edge margin to ensure that it is laterally separatedbefore the filled bags are separated from the web.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention should become apparent from the following description whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a somewhat schematic, fragmentary perspective viewillustrating the cooperation of certain components of the machineutilized in practicing the method of the present invention;

FIG. 2 is a fragmentary side elevational view of a preferred bag formingmachine embodying the present invention;

FIG. 2A is a sectional view taken on line 2A--2A of FIG. 2;

FIG. 2B is a sectional view taken on line 2B--2B of FIG. 2;

FIG. 3 is a plan view of the machine illustrated in FIG. 2 but withportions broken away and sectioned to illustrate details ofconstruction;

FIG. 4 is a schematic illustration of certain machine components in ahome position at the beginning of a bag forming cycle;

FIG. 5 is an illustration, similar to FIG. 4, but illustrating theposition of the components in a preliminary stage of the bag formingcycle;

FIG. 6 is a view, similar to FIG. 4, but illustrating the components ofthe machine in the seaming stage of the bag forming cycle;

FIG. 7 is a view, similar to FIG. 4, but illustrating the position ofthe components upon completion of the bag filling and sealing portionsof the bag forming cycle as the bag is being separated from the web andthe machine components are returning to their home position illustratedin FIG. 4;

FIG. 8 is an enlarged sectional view illustrating primarily the bagseparating assembly of the machine of the present invention in theposition corresponding to schematic FIG. 5;

FIG. 9 is a view similar to FIG. 8 but illustrating the relativepositions of the separating assembly components during the seamingportion of the bag forming cycle as illustrated in FIG. 6;

FIG. 10 is a view, similar to FIG. 8, but illustrating the components ofthe bag separating assembly in the course of rupturing the filled andsealed bag from the web from which it is formed as illustrated in FIG.7; and

FIG. 11 is a greatly enlarged, fragmentary sectional view showing aportion of the horizontal heater bar engaged with the plastic web whileforming the horizontal seams and weakened zone therebetween.

DESCRIPTION OF THE PREFERRED METHOD AND APPARATUS

Referring now to the drawings, FIG. 1 illustrates somewhat schematicallyand in perspective portions of the appratus which is preferably used topractice the method of the present invention. As best seen therein, aweb W of longitudinally folded plastic is fed downwardly in thedirection indicated by the arrow into a machine indicated generally atM, and sealed and filled bags B₁, B₂ fall downwardly from the machine Minto an appropriate receptacle (not shown). Prior to bag closure, partsare charged automatically into each partially formed bag B via a chute Cconnected at its upper end to a hopper (not shown). Primary andsecondary heat sealing jaw assemblies J₁, J₂, respectively are mountedin the machine M for reciprocation laterally with respect to the plasticweb W in the direction indicated by the arrows. Movement of the jawassemblies J₁, J₂ is effected by a linkage mechanism L connected to afluid actuator A, which in the present instance, is an air cylinder. Themajor portion of a bag separating mechanism is located in the region Sof the jaw assemblies J₁, J₂ but is not illustrated in detail in FIG. 1for purposes of clarity. In the illustrated embodiment, continuousdownward tension is applied to the web W as a separated longitudinaledge margin E thereof is stripped from the side of the web W, i.e.,toward the rear in FIG. 1. Appropriate position sensors and electroniccircuitry is provided for controlling the operation of the machine M inthe manner to be described.

Referring now to FIG. 2, the machine M includes a frame 10 whichcomprises upright side panels 10a, 10b extending between upright endpanels 10c, 10d which may be, and preferably are, supported on legs atthe intersections thereof, such as the legs 10e, 10f. The longitudinallyfolded plastic web W is advanced vertically downward through the machineframe 10 centrally thereof by an indexing mechanism of conventionaldesign which both pulls the folded web W from a supply roll and pusheddownwardly on the folded web from above. The folded web W passesdownwardly between the primary and secondary heat sealing jaw assembliesJ₁ and J₂ respectively, which are mounted for reciprocation laterally ofthe web W in the machine frmae 10 on a pair of horizontally separatedparallel guide rods, such as the guide rod 12, extending between theright hand machine frame member 10d and the left hand machine framemember 10c. As best seen in FIG. 3, each jaw assembly, such as theprimary jaw assembly J₁, includes a pair of low friction linearbushings, 14, 15 which slide on the guide rods 12, 13, respectively. Theprimary jaw assembly J₁ extends between the linear bushings 14 and 15and is connected thereto by brackets 16 and 17, respectively. Thecomplementary secondary jaw assembly J₂ is mounted for sliding movementon the guide rods 12 and 13 in a manner similar to the manner in whichthe primary jaw assembly J₁ is mounted, having linear bushings 18 and 19connected to brackets 20 and 21 to which the jaw assembly J₂ isconnected. Thus, when driven, the jaw assemblies J₁, J₂ are capable ofreciprocating laterally with respect to the web W in the directionindicated by the arrows in FIG. 3.

The jaw assemblies J₁, J₂ are driven by the actuator A and linkage Lconnected thereto. To this end, as best seen in FIG. 3, the linkage Lincludes a rocker shaft 25 which extends transversely across the machineframe between the side frame members 10a, 10b. An arm 26 is secured tothe shaft 25 and projects upwardly therefrom. See FIG. 2. The upper end26a of the arm 26 is connected to a rod 27 which is slidably mountedwithin the cylinder portion 28 of the actuator A. The cylinder 28 ispivotally connected to the side frame member 10b as by a trunnion 29(FIG. 3). Thus, retraction of the actuator rod 27 rotates the rockershaft 25 clockwise, and extension of the actuator rod 27 rotates theshaft 25 counterclockwise as indicated in FIG. 2. As best seen in FIGS.2 and 3, the primary jaw assembly J₁ is connected to the rocker shaft 25by a pair of elongate links 30, 31 each of which is connected to a shortarm fastened to the rocker shaft 25, such as the short arm 32 connectedto the link 30. As a result, clockwise pivotal movement of the shaft 25displaces the link 30 leftward and causes the primary jaw assembly J₁ toslide leftward on its guide rods 12 and 13 an amount corresponding tothe angular displacement of the rocker shaft 25.

The secondary jaw assembly J₂ is also displaced by movement of therocker shaft 25. To this end, as best seen in FIG. 3, the rocker shaftarm 32 has an upper end 32b connected to a short link 36 having an endportion which is connected at 36a to a spur 38 projecting from thesecondary jaw assembly bracket 20. The secondary jaw assembly bracket 21is similarly connected to the rocker shaft 25 by spur 39 and short link40. Thus, as best seen in FIG. 2, when the rocker shaft 25 pivotsclockwise from the home position illustrated, the primary jaw assemblyJ₁ moved leftward, and the secondary jaw assembly J₂ simultaneouslymoved rightward toward the centerline C_(L) of the web W.

As the secondary jaw assembly J₂ engages the side of the web W, itsmovement rightward is arrested while leftward movement of the primaryjaw assembly J₁ is permitted to continue. To this end, lost motionconnections are provided between the secondary jaw assembly J₂, links 36and 40, and the machine frame members 10b and 10a, respectively. As bestseen in FIG. 2, the lost motion connections include cams 42 and 44fastened to the frame members 10b, 10a, respectively. Each cam has anL-shaped slot, such as the slot 42a in the cam 42. The cam slotsslidably receive followers 46 and 48 mounted on the ends of the links 36and 40, such as the follower 46 mounted on the end of the link 36 inFIG. 2. The links 36 and 40 are also connected to the secondary jawassembly J₂ by cam followers 36', 39' engaging in vertical slots, 36",39". See FIG. 4. Thus, as the rocker shaft 25 pivots clockwise from itshome position illustrated in FIG. 2, it displaces the secondary jawassembly J₂ righward until such time as the follower 46 engages thebight of the L-shaped camming slot 42a, whereupon the follower 46 movesupwardly. This enables the link 36 to pivot counterclockwise and its pin36' to move upwardly in the slot 36", thereby arresting rightwardmovement of the secondary jaw assembly J₂ while permitting the primaryjaw assembly J₁ to continue its leftward movement toward the centerlineof the web W. Accordingly, movement of the secondary jaw assembly J₂ isarrested at a predetermined precise location with respect to thecenterline C_(L) of the web W.

In accordance with the method of the present invention, the bags B areformed, filled, sealed and separated continuously in the machine M. Eachbag, such as the lower bag B₁ in FIG. 1, is characterized by avertically disposed fold 50 extending along one edge of the bag B₁ and avertical edge seam 51 extending parallel thereto opposite the foldededge 50. A bottom seam 52 extends transversely across the bottom of thebag B₁ and intersects the edges 50 and 51 thereof, and a top seam 53likewise extends across the top of the bag B₁ to define the perimeter ofthe bag B₁.

In the present instance, the web of plastic W is of thermoplastic sheetstock, such as low density polyethylene (LDPE), and the seams 51, 52,and 53 are formed by heat sealing the folded web W between the heatsealing jaw assemblies J₁, J₂. For this purpose, the heat sealing jawassemblies J₁, J₂ are arranged in a generally L-shaped elevationalconfiguration and in vertical planes on opposite sides of the web W. Theheat sealing and anvile portions of the primary and secondary jawassemblies J₁, J₂ are dimensioned so that the vertical seams 51 of aplurality of bags B are formed when the jaw assemblies J₁, J₂ are broughtogether and heat applied therebetween. Simultaneously therewith, thehorizontal heat sealing and anvil portions of the jaw assemblies J₁, J₂form the bottom seam 52 of one bag, such as the bag B₁, the top seam 53of the immediately preceding bag, such as the bag B₂ and a weakened lineof juncture 55 therebetween. See FIG. 11. As will be described, theweakened line of juncture 55 permits the bags to be separated from oneanother when downward tension is applied to a filled bag for therebyrupturing the weakened line of juncture 55.

The web edge E is separated from the longitudinal side seam 51 by aconventional constant tension take-up means, such as a drum 56 thatpulls laterally and downwardly simultaneously with formation of thehorizontal seams 52, 53 from between the jaw assemblies J₁, J₂ while thevertical seam is in a thermally softened state. As a result, the webedge E is continuously attached to the web W above the location wherethe transverse seams are formed, thereby enabling advancing tension tobe applied by the constant tension mechanism, such as indicated at 56(FIG. 1). An indexing mechanism of conventional design cooperates withthe constant tension device to advance the web W downwardly throughpredetermined increments, depending on the desired length of thefinished bag.

Parts are charged into the bag during that period of the forming cycleafter which the side seam 51 and bottom seam 52 have been formed butbefore the web W is indexed downwardly and the top closure seam 53formed. During this period, the web is gripped above its bottom seam 52to protect the same by preventing falling parts from striking the seam52 prematurely and thereby ripping the same. The grip is released justprior to indexing of the web.

Web indexing occurs in timed relation with the movement of the heatsealing jaw assemblies J₁, J₂. The timing is predetermined to allowsufficient time for the bottom seam 52 and side edge seam 51 to set upwithout allowing sufficient time for the weakened line of juncture 55between the transverse seams to become sufficiently strong as to make itdifficult to separate the bags from the web by rupturing the same in themanner described. By way of example, and not by way of limitation, for athermoplastic web W of LDPE having a thickness of 2 mils., a preferredheating cycle is about 0.2 to about 0.4 seconds with the heating jawassemblies J₁, J₂ in contact with the sides of the web W under apressure of about 200 psi. and at a heating jaw surface temperature ofabout 350° F. to about 400° F. Parts are charged from the chute C intothe partially thus-formed bag while the web is still gripped and beforethe jaw assemblies J₁, J₂ begin to separate from the web W. Bags areformed, filled, sealed, and separated at a rate of about 50-60 finishedbags per minute.

For purposes of explanation, the jaw assembly which carries the heatingelements is regarded as the primary jaw assembly J₁, and thecomplementary jaw assembly which serves as a back-up for the primary jawassembly J₁ is regarded as the secondary jaw assembly J₂. The actuator Aand related web indexing apparatus, the heating cycle power and timing,and sealing pressure, among other functions, such as position sensing,is automatically controlled by a programmable controller which operatesthrough various electronic sensors, solenoid air valves, and relatedmechanisms to effect the desired sequential operation of the variouscomponents of the machine M in the manner described. Since thecontroller utilzies state of the art electronics, it will not bediscussed in detail herein except to the extent necessary to explain thefunctional interaction of the various machine elements.

As best seen in FIG. 2, the primary jaw assembly J₁ is illustrated inFIG. 2A, and the secondary jaw assembly J₂ is illustrated in FIG. 2B.FIG. 2A is a view looking rightward in FIGS. 2 and 3, and FIG. 2B is aview looking leftward in FIGS. 2 and 3. The web W is superimposed inphantom lines in FIG. 2A to illustrate its relationship to the primaryjaw assembly J₁.

Referring now to FIG. 2A, the primary jaw assembly J₁ includes a platen60 mounting a vertical heater bar 61 along one side portion thereof anda horizontal heater bar 62 along the lower portion thereof. Thehorizontal heater bar 62 has a left hand end portion 62a which underliesthe lower end portion 61a of the vertical heater bar 61. The horizontalheater bar 62 extends completely across the width of the web W and, inthe illustrated embodiment, therebeyond for a sufficient distance toenable webs of various widths to be accommodated within the machine M.The vertical heater bar 61 extends upwardly from the horizontal heaterbar 62 a distance corresponding to at least two bag lengths (measured inthe vertical direction) as indicated by the lines L₁, L₂ in FIG. 2A.

Preferably, each heater bar, such as the vertical heater bar 61, isprotected from direct contact with the web W by a movable sheath T₁ ofpolytetrafluorethylene (Teflon) material which is carried in a dispenser63 mounted on the backside of the platen 60. The sheath T₁ is advancedmanually periodically by means of a knurled knob 64 which is connectedto a vertically elongate shaft around which the Teflon material iswrapped after passing from its storage dispenser 63 and about the nose61b of the vertical heater bar 61. Although not illustrated, a similarmeans is provided for advancing the lower Teflon sheath T₂ which coversthe horizontal heater bar 62. Preferably the shaft about which thehorizontal Teflon sheath T₂ wraps is connected to the vertical shaftabout which the vertical Teflon sheath T₁ wraps by means of rightangular bevel gears so that rotation of the knob 64 causes both thevertical and horizontal take-up shafts to rotate simultaneously. In theillustrated embodiment, the heating elements 61 and 62 are eachpreferably powered by 120 VAC proportional type (Triac controlled)electrical current which develops a surface temperature of about 350° F.to about 400° F. with a power consumption of about 150 watts. As wellknown in the art, the Teflon sheaths prevent the heater bars fromsticking to the web W.

In order to stabilize the web W as the bag seams are being formed whileenabling the web W to be stripped from the sheathed heater bars 61, 62,a pair of elongate stripper bars 65a, 65b are provided in spacedparallel relation on opposite sides of the vertical heater bar 61. Inlike manner, a pair of horizontal stripper bars 66a, 66b extend inspaced parallel relation on opposite sides of the horizontal heater bar62. The vertical stripper bars 65a, 65b are mounted to and projectupwardly from the upper horizontal stripper bar 66b for movement inunison therewith.

The stripper bars 65a, 65b and 66a, 66b are each mounted for elasticmovement relative to their associated jaw assemblies. To this end, anair spring 68, best seen in FIGS. 8, 9 and 10, and guide pins (notshown) mount the two vertical stripper bars 65a, 65b and the upperhorizontal stripper bar 66b to the primary jaw platen 67. The lowerstripper bar 66a is similarly elastically connected to the platen panel67, by a helical compression spring such as indicated at 69 in FIG. 8.For purposes to be discussed, the lower stripper bar 66a is provided bya knurled roller mounted for rotation at its opposite axial ends in lowfriction bearings each of which is mounted to the end of a rod, such asthe rod 70 connected to the spring 69 and illustrated in FIG. 8. Thus,both the horizontal and vertical stripper bars 65a-66b of the primaryjaw assembly J₁ are normally disposed in a forwardly projected positionwith respect to the primary jaw platen 67 and they are biased forwardlyof their associated heater bars.

The secondary jaw assembly J₂ has anvils which cooperate with thestripper bars 65b and 66b to form the side edge and transverse seams inthe web W. To this end, as best seen in FIG. 2B, a vertically elongateanvil bar 75b is mounted to the secondary jaw platen 76, and as bestseen in FIG. 3, the anvil bar 75b is juxtaposed with respect to thestripper bar 65b on the primary jaw assembly J₁, being aligned therewithso that they operatively engage the folded plastic web W therebetween. Ahorizontal anvil bar 77b is similarly mounted to the secondary jawplaten 76 in juxtaposition with the horizontal stripper bar 66b of theprimary jaw assembly J₁. See FIG. 3. As best seen in FIG. 3, an anvilbar 78 extends vertically in spaced parallel relation with the verticalanvil bar 75b and is aligned with the nose 61a of the heater bar 61 onthe primary jaw assembly J₁. Similarly, a horizontally elongate anvilbar 79 is provided below the horizontal anvil bar 77b and is alignedwith the nose 62a of the horizontal heater bar 62. See FIGS. 8 and 9.

As best seen in FIG. 8, the upper secondary jaw assembly anvil bar 77bis biased rightward away from its mounting platen 76 as by an airoperated fluid actuator 80. The lower secondary jaw anvil bar 79 isrigidly affixed to platen 76 and moves therewith. With this structure,when the web W is interposed between the vertical heater bar 61 and itscounterposed anvil 78, and heat and pressure applied, the vertical bagseam 51 is formed. As the seam 51 is being formed, the edge E issimultaneoulsy separated therefrom by being pulled laterally due to thesoftening of the thermoplastic material of the web W.

As best seen in FIG. 11, the bottom seam 52 and top seam 53 (FIGS. 1 and2A) are simultaneously formed when the horizontal heater bar 62 engagesthe web W and presses it against its anvil 79. As the top and bottomseams 52 and 53 are being formed, the web W is being provided with aweakened line of juncture 55 between the seams 52 and 53 due to thesoftening of the thermoplastic web W caused by heat and applied pressureand the somewhat sharp nose portion of the heater bar 62. During theheating portion of the cycle, pressure on the web W is increased byautomatically increasing the pressure of the air admitted into theactuator cylinder 28. The increase in air pressure, of about 200%,ensures adequate seam formation and softening of the web W along theweakened line of juncture 55. Thus, not only does the single actuatorcylinder 28 drive the jaws J₁, J₂, but it also enables the desired jawengagement pressures to be controlled automatically.

The filled bag is separated along the weakened line of juncture 55 whentension is applied thereacross during the bag separating portion of thebag forming cycle. To this end, separation is effected by rupturing theweb W along its weakened line of juncture 55 while the thermoplasticmaterial is relatively soft and weak. By utilizing a rupturing action toeffect separation, knives, hot wires and the like are eliminated,thereby eliminating the proclivity for such conventional cuttingmechanisms to malfunction and require frequent periodic cleaning due tomelted plastic accumulating thereon.

The bag separating mechanism may best be seen by reference to FIGS.8-10.

Referring first to FIG. 8, the bag separating mechanism, the location ofwhich is indicated generally by S in FIG. 1, includes the lowerseparator bar roller 66a which engages laterally against the right sideof the web W below the point of engagement therewith of the horizontalheater bar 62 and its back-up anvil 79. Juxtaposed with the bar roller66a is a nip platen 85 mounted for pivotal movement about a horizontalaxle 86 carried by the secondary jaw assembly J₂. The nip platen 85 hasa forwardly projecting nose 85a which, as best seen in FIG. 10, isadapted to engage laterally against the left side of the web W and tooverlie a portion of the bar roller 66a when it is operatively engagedwith the nip platen 85. The nip platen 85 is biased in a clockwisedirection about its axle 86 by an extension spring 87 connected to thenip platen 85 rearwardly of its axle 86 and behind the horizontal anvil79.

For purposes to be described, a cam roller 88 is mounted for rotationcoaxial with the point of attachment of the lower end of the extensionspring 87 to the nip platen 85, and a rearwardly and upwardly inclinedcamming surface 89 is provided on the actuator rod 82. When the cammingsurface 89 is engaged with the cam roller 88 in the manner illustratedin FIG. 8, the nip platen 85 is maintained in its retracted position,i.e. as shown in FIG. 8. This is the relative position of the bagseparating elements when they first are displaced into lateralengagement with opposite sides of the web W. In such position, thesecond horizontal separator bars 66b and 67b are urged into abuttingengagement with the web W therebetween, thus frictionally gripping theweb W.

The lower heater bar anvil 79 laterally engages the web W while itscooperating horizontal heater bar 62 is spaced laterally therefrom. Thenose 85a of the nip platen 85 is engaged with the left side of the web Wand the lower spreader bar roller 66b is engaged with the right side ofthe web W opposite the separator platen 85. This is the relativeposition of the machine elements at the start of the bag making cycle asillustrated schematically in FIG. 5 after having been displacedthereinto from the home position illustrated schematically in FIG. 4,and as illustrated in FIGS. 1 and 2. As discussed above, this motion ofthe machine elements occurs when the fluid actuator A is pressurized topull its operating rod 27 inwardly and thereby pivot the rocker shaft 25clockwise.

During the next phase of the bag making cycle, the fluid actuator Acontinues to pull its operating rod 27 inwardly. As this occurs, theprimary jaw assembly J₁ continues to move leftward toward the centerlineof the web W, such as in the manner illustrated schematically in FIG. 6.When the primary jaw assembly J₁ reaches the limit of its excusion, thevertical and horizontal heating bars 61 and 62 engage the web W and arebacked-up by their complementary anvils, and heat is applied to the webW therebetween for forming the vertical seam 51 and horizontal seams 52and 53 as discussed heretofore. This may best be observed by referenceto FIG. 9, wherein the horizontal heater bar 62 is shown engaged againstthe right side of the web W and its cooperating anvil 79 engaged againstthe left side thereof. In this position, it will be noted that the lowerroller 66a is engaged against the right side of the web W and the nipplaten 85 is engaged against the left side of the web W, forming a niptherewith.

After a heating cycle of predetermined duration, such as discussedabove, the acutator A is cycled in the reverse direction and itsoperating rod 27 extended. This causes the rocker shaft 25 to rotate inthe counterclockwise direction, such as in the manner illustrated inFIG. 7. During such movement, the vertical stripper bars 65a, 65b, 75binitially remain engaged with opposite sides of the web W while thehorizontal stripper bars 66b and 77b cooperate to grip the web Wtherebetween. The elastic connections between the horizontal stripperbars 66b and 77b and their respective mounting platens permit them toremain engaged with the web W on its centerline C_(L) as the platensseparate due to the reverse rotation of the rocker shaft 25. As theplatens separate from one another, the lower anvil 79 separates from thehorizontal heater bar 62, since these elements are non-relativelymovably carried by their movable platens. As the platens 67, 76 continueto separate, the movable nip platen 85 begins to pivot in the clockwisedirection about its axle 86 causing its associated roller 66 b to rotateabout its axis. This motion creates a downward tension on the filled bagand thereby ruptures the same along the weakened line of juncture 55described above. The nip platen nose 85a ensures a positive separatingaction. See FIG. 10.

After the movable platens 67, 76 return to their home positions, such asillustrated schematically in FIG. 4, the nip platen fluid actuator 81 issignalled to move leftward, as by air pressure being introduced to therod end of the piston thereof. This causes the camming surface 89,engaged with the cam roller 88, to pivot the nip platen 85counterclockwise about its axile 86 for returning it to its retractedposition illustrated in FIG. 8. Simultaneously, the horizontal separatorbar 77b is retracted due to the interengagement of a tang 82a on theactuator rod 82 with a shoulder 77' on the underside of the horizontalseparator bar 77b. This action ensures release of the filled bag fromthe bag 66b and nip platen 85, permitting the bag to drop freely bygravity into an appropriate receptacle. Thereafter, the web W is indexeddownwardly and the cycle repeated.

To prevent too much air from being contained in the bag before its topseam is formed, the filled bag is compressed slightly between a back-upplate 90 carried on the secondary jaw assembly J₂ and an elastic pack,such as a sponge 91 carried on the primary jaw assembly J₁. See FIG. 2.The back-up plate 90 and elastic pad 91 are juxtaposed on opposite sidesof the filled bag and are movably mounted relative to their respectivejaw assemblies by small fluid actuators, or air cylinders, 92 and 93,respectively. The fluid actuators 92, 93 are operatively connected inthe control circuitry to retract quickly after making initial contactwith the filled bag to ensure that only sufficient pressure is appliedto the partially filled bag to expel the air but not to damage the bagor parts contained therein.

If desired, the machine M can be used to form bag headers. This isaccomplished by modifying the control circuitry to provide a pair oftransverse seams in spaced parallel relation at the upper end of thebag. For instance, the lower one of the seams provides the top bagclosure while the upper one of the seams, being spaced verticallytherefrom, cooperates therewith to form a margin at the top of the bag.Preferably, printed bag material is used having printing in zonescorresponding to the locations of the headers.

In view of the foregoing, it should be apparent that the presentinvention now provides an improved method and apparatus for continuouslyforming, filling, sealing and separating bags from a web ofthermoplastic sheet material. The method and apparatus functionsefficiently with minimal operator supervision to produce filled bags ina relatively high speed manner. The apparatus is relatively simple inconstruction, and therefore highly reliable in operation. Because of itsrelative simplicity, the apparatus can be manufactured and operatedeconomically.

While a preferred method and apparatus have been described in detail,various modifications, alterations and changes may be made withoutdeparting from the spirit and scope of the present invention as definedin the appended claims.

We claim:
 1. Apparatus for filling plastic bags formed from a web ofplastic material, comprising:frame means for receiving said web, meansfor guiding said web in a longitudinally folded manner downwardly intothe frame means, complementary heat sealing jaw means mounted in saidframe for lateral reciprocation relative to said folded web to provide alongitudinal side seam and a transverse bottom seam cooperable with saidfolded web to provide an upwardly open pocket and to form a transversetop seam for closing the pocket after the web has been advanceddownwardly a predetermined extent relative to the frame means, drivemeans connected to said heat sealing means for effecting saidreciprocation thereof and for applying to said web a predeterminedpressure for forming said seams, gripper means carried on said jaw meansfor releasably engaging opposite sides of said web above the location offormation of said top seam of said pocket, and separator means mountedin said frame means below said gripper means for frictionally engagingopposite sides of said web below the location of formation of said topseam therein and cooperable in timed relation with said heat sealingmeans during formation of said top seam to tension said weblongitudinally and thereby to cause a filled and closed bag to be formedand separated from the folded web, whereby plastic bags are filled andclosed in a continuous manner.
 2. Apparatus according to claim 1including shaped surface means on said complementary heat sealing meanscooperable during formation of said transverse top seam on said pocketto simultaneously form said transverse bottom seam on an immediatelyupstream pocket and to provide a weakened line of juncture between saidtop and bottom pocket seams for permitting said bag to be separated fromsaid web when said tension is applied by said separator means. 3.Apparatus according to claim 2 wherein said shaped surface meansincludes a flat platen and a tapered nose which cooperate tor form saidtop and bottom pocket seams on opposite sides of said weakened line ofjuncture.
 4. Apparatus according to claim 3 wherein said separator meansincludes a roller laterally engaging said web adjacent to the locationof formation of said top seam and rotatable about a horizontal axis, andnip means juxtaposed with said roller on the opposite side of said webfor creating friction between said web and said roller, and means forrotating said roller about its axis for frictionally tensioning said webdownwardly to separate said filled bag therefrom.
 5. Apparatus accordingto claim 4 wherein said nip means includes a nip platen normallydisposed alongside said web and engaging said opposite side of said web,and means for moving said nip platen relative to said roller axis forrotating said roller and thereby tensioning said web to effect said bagseparation.
 6. Apparatus according to claim 5 wherein said nip platenmoving means includes means mounting said platen to pivot about ahorizontal axis below the rotational axis of said roller, and means forpivoting said platen about its axis.
 7. Apparatus according to claim 6wherein said platen pivoting means includes means for biasing saidplaten toward said roller and web and for pivoting the platen about itshorizontal axis, and means for returning said platen to its normalposition alongside said web after separation of said bag therefrom. 8.Apparatus according to claim 7 including means for biasing said rollerinto continuous engagement with said nip platen during said pivotalmotion of said platen toward said roller.
 9. Apparatus according toclaim 8 wherein both said nip platen and said roller are carried on saidheat sealing means and are movable relative thereto to effect said bagseparation as said complementary heat sealing means move away from saidweb.
 10. Apparatus according to claim 9 wherein said nip platen has alaterally extending protrusion engaging said folded web below saidweakened line of juncture and above said roller for aiding in separatingsaid web from said gripping means as said heat sealing means separate.11. Apparatus according to claim 1 wherein said drive means includes arocker shaft pivotally mounted in said frame alongside said folded web,linkage means connecting said rocker shaft to said complementary heatsealing means for causing said heat sealing means to move toward saidfolded web when said rocker shaft is pivoted in one direction and awayfrom said folded web when pivoted in the opposite direction, a fluidpressure operated actuator connected to said rocker shaft for pivotingthe same in said opposite directions, and means for increasing the fluidpressure in said actuator as said complementary heat sealing meansadvance into close proximity with one another to form said pocket seams.12. Apparatus according to claim 11 wherein said complementary heatsealing means includes a heater member and an anvil member both mountedfor sliding movement toward and away from one another in said frame, alink connecting one of said members to said shaft and lost motionlinkage means connecting the other of said members to said shaft, saidlost motion linkage means causing its connected member to stop moving ata predetermined location with respect to said web while said link causesthe other member to continue moving as said rocker shaft pivots. 13.Apparatus according to claim 12 wherein said lost motion linkage meansincludes an angulated cam surface mounted to said frame and a camfollower engaging said cam surface and movably mounted to its connectedmember for movement vertically with respect to its normal path ofmovement as it approaches the folded web.
 14. Apparatus according toclaim 1 wherein the portion of said complementary heat sealing meansthat forms said longitudinal side seam extends for a distance which isat least about twice as long as the side seam formed in a single bag andextends along said folded web inwardly of its edges so that a pair ofedge margins are formed between said side seam and the edges of thefolded web, and including means for pulling said edge marginslongitudinally and laterally of said web for separating said web edgemargins from the web during forming and filling of the bags. 15.Apparatus according to claim 14 wherein said pulling means includes aconstant tension take-up roller engaging said web edge margins andtensioning the same continuously so that the edge margins are separatedfrom the web before the filled bag is separated therefrom.
 16. Apparatusaccording to claim 15 wherein said top and bottom seam forming portionsof said heat sealing means extend less than completely across the widthof the folded web from its folded side.
 17. Apparatus according to claim1 wherein at least one of said complementary heat sealing means has aheated zone, and including a layer of tetrafluoroethylene fabricinterposed between said heated zone of said heat sealing means and saidweb, and means for periodically advancing said fabric relative to saidheated zone.
 18. In apparatus for forming and filling plastic bags,including means for guiding a longitudinally folded web of plastic as itdescends vertically, complementary laterally movable heat sealing meanscooperable to provide transverse and longitudinal seams in the foldedweb for defining therein an upwardly open pocket and to form a closurefor the pocket after having been loaded by gravity, and means forsubsequently separating the loaded pocket from the web, the improvementwherein said pocket separating means comprises means for gripping theweb transversely above the transverse seam forming the pocket closure,and means cooperable with said heat sealing means after a predeterminedheating time interval for applying tension to said pocket longitudinallyof the web and thereby rupturing the loaded pocket from the web. 19.Apparatus according to claim 18 wherein said web tensioning meansincludes means providing a roller engaging one side of said web, meansproviding a nip on the opposite side of said web in juxtaposition withsaid roller, and means for effecting rotation of said roller for pullingon said web.
 20. Apparatus in accordance with claim 19 wherein said nipproviding means includes a planar surface disposed vertically alongsidethe web opposite the roller, and means for displacing said surfacerelative to the rotational axis of the roller for effecting said rollerrotation and thereby tensioning the web.
 21. Apparatus according toclaim 20 including means for pivoting the nip surface and means forbiasing the roller laterally toward said nip surface with the webengaged therebetween for thereby effecting said rotation of the rollerand said tensioning of the web.
 22. Apparatus according to claim 21wherein said nip forming surface has a finger protrusion overlying atleast a portion of the roller for engaging the web laterally above theroller to aid in separating the loading bag from the web.
 23. In amethod of forming and filling bags from a downwardly advancing web ofplastic which is longitudinally folded to form a fold line and a pair ofedges spaced therefrom, the improvement comprising the steps of:heatsealing said web longitudinally inwardly adjacent to said edges to forman elongate side seam having a length at least as long as two filledbags, simultaneously with the formation of said side seam, heat sealingthe web transversely to form a transverse seam having a heat weakenedcentral portion located between the bottom of one pocket and the top ofa precedingly formed pocket, loading the one pocket from above, grippingthe loaded pocket transversely above its bottom seam, and while saidtransverse seam is in its heat weakened condition, tensioning the webfrom below for rupturing said web along said weakened portion andthereby separating a filled bag from the web.
 24. A method according toclaim 23 wherein said web tensioning step is effected by frictionallyengaging said web between a roller and a nip platen, and while biasingthe roller and nip platen toward one another, displacing the nip platenrelative to the rotational axis of the roller.
 25. A method according toclaim 24 wherein said longitudinal seam is spaced inwardly from said webedges and said transverse seam formed in said web extends transverselyfrom the longitudinal fold to at least said longitudinal seam but shortof said web edges to form an edge margin, and including the step ofcontinually pulling said edge margin downwardly and laterally withrespect to said web for separating said web edge marging from the foldedweb before said filled bags are separated from the web.